Type inference

fact ::	(Num a) => a -> a
n ::	(Num a) => a

        fact 0 = 1
        fact n = n * fact(n-1)

"Okay, everything checks out!"

• And if you ask it, it will tell you the type of fact:

        fact :: (Num a) => a -> a

• If you ask for the factorial of an Integer, you get back an Integer

• If you ask for the factorial of a Float, you get back a Float

• If you ask for the factorial of a String, you get a compile-time error

• Because String is not an instance of Num

Next

Copyright © 1999,2008 Mark Dominus